I don't cut my scraps into any sizes. I just leave them however they are. I never know when I'll need dragonfly wings or a dozen leaves or some other applique shape. I also use my scraps for small wall hangings that use both applique and piecing. I have no idea what I'll need six months from now and if it's all cut into specific sizes I may not be able to get that 3 inch strip from the perfect fabric if I've already cut it into 2.5 inch strips.
That's what suits me. You do what suits you.